Comminution system for wet solid materials



E. c. MILLER Oct. 3, 1961 COMMINUTION SYSTEM FOR WET SOLID MATERIALS Filed April 21, 1958 w Nu .m m R1 /1 M 3 mm W f 6 Z T a a Filed Apr. 21, 1958', Sen No. 729,666

2 Claims. (Cl. 110-406) v This invention relates to a comminution system for wet solid materials, and more particularly for apparatus ror use with a steam. generating unit for pulverizing solid fuels having a high surface moisture content.

It has long been recognized that the capacity of a pulverizer will decrease whenever surface moisture is associated with the material entering the machine, and that a large percentage of surface moisture in the material may even render it impossible for the machine to operate at all. Various remedies have been suggested, including the provision of a drying apparatus to remove excess moisture from the material before itenters the pulverizer. Another suggestion presented in the past involves introducing into the palverizer heated air or other gas to aid in drying the material and to carry the fine material out of the machine. A drying apparatus is an expensive piece of equipment and it is often dificult and complicated to operate. in many installations it is not economically ustified, since the excess moisture conditions may be encountered rather infrequently. While the feeding of hot gas to the pulverizer is helpful in. some. conditions, there are'many situations where this is not adequate to overcome the difficulties related to the use of a very wet fuel. These and other difficulties experienced with prior art devices have been obviated in a novel manner by the present invention.

it is, therefore, an outstanding obiect of the invention to provide an, apparatus capable of cornminuting wet solid material to a fine powder at a very high rate in proportion to the size of the apparatus.

it is a further object of this invention to provide, in combination with a pulverizer of known construction other apparatus which will greatly increase the capacity of the pulverizer.

It is a still further object of the present invention to provide an apparatus for producing a fine powder from solid material and having a very high capacity in pro portion to its size, the construction being such that no appreciable reduction in capacity will take place, even though the moisture content of the material as received may increases greatly.

Another object of theinstant invention is theprovision of apparatus adapted for comminuting coal or similar solid fuel and delivering the fuel. as a fine powder to a furnace for combustion, the capacity of the apparatus being affected very little by a considerable increase in the amount oi surface moisture in the coarse fuel.

Although the-novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself as to its objects and advantages, the mode of its operation, and the manner of its organization, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which:

The single figure is a somewhat schematic view of apparatus embodying the principles of the present invention.

Referring to the drawing, it can be seen that a steam generating unit, indicated generally by the reference numeral it is shown in use with a pulverizer 11. The steam generating unit is of the general type shown and described in the patent of Miller et al. No. 2,800,888

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and is provided with a steam-and-water drum 12, a lower drum 13, and a combustion chamber 14 having a burner 15 of the flare type. The pulverizer 11 is generally of the type shown and described in the patent to Rogers No. 2,699,898 and is of the attrition type. The steam generating unit discharges combustion gases into an air heater is leading through a duct 17 and through an induced draft fan 15 leading to a stack 19. A positive draft fan 21 introduces air into the air heater 16 where it passes in heat exchange relationship to the gases passing there through and the air thus heated passes through a duct leading to the air box 23 associated with the burner Underlying the coal bunkers or other source of fuel supply, not shown, is a hopper 24 leading to a drum-type feeder 25. An output chute 26 of the feeder is connected to the inlet of a crusher 27 which is of the type generally shown and described in the patent of Rogers No. 2,647,695. The crusher has rotating hammers 28 under which is situated the usual grid 29. A hopper 31 underlies the grid and has an outlet chute 32 at one side leading through a gas valve 33 to a chute 34 connected to the inlet of the pulverizer 11; the gas valve 33 is of the rotating drum type which is capable of passing solid material without escape of gas thereby. A duct 35 is connected to the outlet of the pulverizer ill and leads to the burner 15 A damper 36 is located in this duct and serves to control the flow of fuel and air therethrough.

A duct 3t) is connected at one end to the duct 22 leading to the burner box 23 and at the other end to an inlet fitting 3'7 extending upwardly from the housing of the crusher 27. A damper 38 provides for control of flow of gases through the duct. A duct 39 leads from a point in the duct 30 between the duct 22 and the damper 38 to a point in the chute 34 at its intermediate point, there being a damper 41 located in the duct 39 to control the flow of gases therethrough. One wall of the hopper 31 associated with the crusher 2'7 is inclined and is provided with staggered flat, horizontal plates 42 arranged to that fuel tends to fall downwardly along the surface while gases may pass laterally between the plates 42. A large duct 43 leads away from the hopper and located in the duct is a conical separator44 of the axial type. As is evident in the drawings, the separator 44 comprises a large conical member 45 from which tabs 46 are pressed radially outwardly. The ends of the tabs are directed toward the crusher 27 and the hopper 31 so that the tendency is for the mixture of powdered fuel and air to pass through the separator with the fuel staying within the cone and the air passing outwardly through the apertures left by the formation of the tabs 46. The smaller end of the separator 45 is connected by a duct 47 to the chute 34- iust below the gas valve 33, and a damper 48 is inserted in the duct to control the flow therethrough. Further along the duct 43 is attached to one end of a duct 49, the other end of which is connected into the combustion chamber 14 of the steam generating unit. A damper 51 is located in that duct and controls the flow of gas therethrough. The duct 43 continues past the duct 49 and is eventually connected to the duct 17 leading to the stack 19 and a damper 5 2 is located in the duct to control the flow of gas therethrough.

The operation of the apparatus will now be readily understood in view of the above description. Fuel enters the system through the hopper 24- and its introduction is controlled by means of the drum-type feeder 25 which may, on occasion, contain a very high percentage of surface moisture. One example of such a fuel is lignite; similar low-quality fuels fall into the same category. The fuel falls through to the crusher 27 where it is comminuted by the hammers 28 and when its size is reduced sutficiently it passes through the grid 29-. Actually,

the action in the crusher 27 is most important to the drying action because of the agitation to which the particles of fuel are subjected. Hot air originating in the fan 21 is heated in the air heater 16, passes through the duct 22, and then passes through the duct 30 into the crusher under the control of the damper 38. The mixture of hot air and fuel is subjected to agitation by the hammers 28, thus causing a considerable portion of the moisture in the fuel to be vaporized and to enter into the air. The partially dried and roughly comminuted fuel and air pass downwardly through the grid 29 into the hopper 31. The fuel falls downwardly along the plates 42, but the air, because of the positive pressure in the system, tends to go through the plates and pass axially along the duct 43. The fuel passes downwardly and goes through the gas valve 33 into the chute 34. The air, containing water vapor and also a considerable amount of fine particles of fuel, enters the separator 44 where the fuel is forced inwardly of the conical member 45 and passes into the duct 47 while the air passes outwardly around the tabs 46 and continues to flow along the duct 43. The fuel which passes into the duct 47 is controlled by the damper 48, there being an amount of air sufficient to carry the fine particles of fuel along the duct. This fuel with a small quantity of air mixes with the fuelwhich has passed through the gas valve 33 and the two. streams merge in the chute 34 and enter the pulverizer 11.

Hot air originating in the duct 22 passes through the duct 39 under the control of the damper 41 and mixes with the fuel descending through the chute 34. Therefore, warm air with a very low relative humidity mixes with the fuel and enters the pulverizer. The amount of fuel and air leaving the pulverizer through the duct 35 is controlled by e damper 36; eventually the stream of fuel and air enters the burner and is burned in the combustion chamber 14. The moist air which was separated by means of the plate 42 and the separator 44 continues along the duct 43 and passes through the duct 49 under the control of the damper 51 for projection into the combustion chamber 14. This air may have a fairly high amount of fine particles of fuel and, of course, it contains a considerable amount of heat, as well as vaporized water. Any portion of this air which it is not desired to introduce into the furnace combustion chamber passes along the duct 43 under the control of the damper 52 and enters the duct 17 for projection up the stack 19. In a specific example, wet coal containing 66% surface moisture is fed through the drum-type feeder 25 while drying air at 600 F. enters the crusher 27 through the duct 36 in the amount of 2 pounds of air per pound of fuel. After separation in the bars 42 and the separator '44, the clean, wet air has been reduced in temperature to around 200 F. and the coal which passes downwardly through the chute 34 contains about 50% moisture. Assuming that the exit temperature of the air and fuel leaving the pulverizer in the duct 35 is 400 F., the efiiciency of the pulversizer would be 68%. This is to be compared with the efficiency of 55%, if the 66% moisture coal was to be introduced directly into the pulverizer. If one were to assume that all of the air passing through the duct 43 was projected into the stack 19 and none was introduced 'into the combustion chamber 14, this would result in a 'loss of about 6% efiiciency due to the heat in the air, so that the net gain by use of the present apparatus --aooawa permitting the said air without passing through would be 68%, minus 55%, minus 6%, or 7% efliciency. This percent of gain, of course, would be considerably greater if some or all of the air were intro' duced into the combustion chamber as could be readily the case.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions, and changes in the forms and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

The invention having been thus described what is claimed as new and desired to secure by Letters Patent is: 11. A comminution system for wet solid fuel, comprising a furnace into which the fuel is to be fired, a fuel feeder, a crusher providing for a coarse comminution and agitation of the fuel, a first conduit for introducing gain in dry, heated air into the said crusher, a pulverizer pro- .Viding for a fine comminution of the fuel, means causing a flow of fuel between the crusher and the pulverizer, a primary separator interposed in the flow of fuel between the crusher and the pulverizer to remove the said air from the fuel, a second conduit connected at one end to the furnace and at the otherend to the primary separator for to pass directly to the furnace the pulverizer, a secondary separator in the said second conduit removing fine particles of fuel from the air, a third conduit connecting the secondary separator to the pulverizer for returning the fine particles of fuel so removed to the pulverizer, and a fourth'conduit connected at one end to the pulverizer to introduce. dry, heated air therein.

2. A comminution system for wet solid fuel, comprisinga furnace into which the fuel is to be fired, a stack connected to the furnace, a fuel feeder, a crusher providing for coarse comminution and agitation of the fuel, a source of dry heated air, a first conduit connecting the said source and the crusher for introducing dry heated air therein, a pulverizer providing for a fine comminution of the fuel, a chute connecting the crusher and pulverizer for the flow of fuel therebetween, a primary separator connected in the said chute and interposed in the flow of fuel toremove the said air from the fuel, a second conduit connected at one end to the primary separator and at the other end to the furnace for permitting the said air to pass directly to the furnace and to the stack without passing through the pulverizer a secondary separator mounted in the said second conduit for removing fine particles of fuel from the air, a third conduit connected between the secondary separator and the said chute for returning the fine particles of fuel so removed, and a fourth conduit at one end connected to the said chute to introduce dry heated air therein for mixture with the fuel and introduction into the pulverizer.

References Cited in the file of this patent UNITED STATES PATENTS 

